I'd go for the balsa in this case. Easy to shape, and phenomenal compression strength (end grain). Honeycomb might be a pain unless it is foam filled or used with prepreg.

Should be an incredible project - I can't wait to see it...

Chris,

Yes the shaping has me headed for balsa as thats a lot of tapers, maybe next project I'll look at some of the foams (dinylcell, etc), has great compression strength and reasonable shear resistance. Wish I could figure out a nifty way to screw them on.
JS

I have done several projects by vacuum bagging the fins. But I have yet to do balsa or double wedge shaped. I usually start with a foam or honeycomb composite to start with and then vacuum bag more carbon and fiberglass after finishing the edges. It has worked great and is exceptionally strong.

Doug

I've done several projects with multilayer, multiple fabric on honeycomb and on balsa. Most vacuum bagged, a couple pressed between sheets of 3/4" particle board with my car parked on top. Works great.

For your app, I'd make the cores out of blue or pink styrofoam and do a bunch of layers of fabric on each side. Use a hotwire cutter to create the double diamond airfoil in the foam, then wrap the edges with glass. You'll probably want to embed a root edge and central rib out of wood of some sort for bonding strength to the airframe and if they're through the wall, the entire tab should be wood. Then 3 or 4 layers of carbon or carbon/kevlar topped by glass.

Just my quick two cents.

Warren

Warren,

Thanks, I don't know why i can't overcome my resistance to hot wire cutting--looks simple enuf, just a variable d/c supply with running thru some heavy nichrome right? Want the wire a dusky red. And its not like this is some fancy NACA airfoil. But for some reason I have more confidence in using a belt sander on a balsa slab to get it right. 😕

I like your idea of a tang/rib down the middle, and using stronger material for the tab if TTW. Still hoping for some inspiration on some way to make these bolt on. Otherwise its a coffin sized crate to get to vegas and reno this year. Whether balsa or blue foam, its gonna get a nice plate for skin. I'm thinking for this app, of buying some cheap 10 oz e glass FG from e-bay (2 bucks/yard with some irregularities) and sandwiching bout 6 layers per side between one of kev on the inside and CF on the outside. Doing so, should result in a pretty strong fin, at about $20/fin.

You should post the car idea on composites forum on current thread, that will get some grins...
JS

the thing about hot wire is you also get a negative to nest the fin in when pressing or what ever. I also have seen just pink or blue foam with carbon and FG with no spar through the wall design glued to the motor tube. you have to keep in mind the surface area that a 3/8 in thick fin compared to a 1/4 in. adding a spar you add weight, if that is OK the it will make it stronger but a good composite lay-up will do for most projects through K. Ken Mizoi is a good example of someone that used foam to get a shape and then covered it with CF and FG for many different rockets including the Hermes.

James,

A nest would make grinding the airfoils a lot easier, no doubt. And cheap, perfect crating material to boot. It all comes down to what you trust--I have done FRP reinforced balsa. I was very, very impressed by the strength/wt ratio.

I need to learn to cut foam but maybe in the context of some boost glider. Then when I have those skills....
JS

PS: I had one contact with Kim M at a Coyote hunt a few years back. Dale N. set the fly by getting me out there, and Ken pulled the hook so bad, I thought of nothing but rockets and sex for a week. As a relatively recent divorcee, two channels was a major diversion.